Generator

ABSTRACT

An electric generator  10  of the present invention comprises a permanent magnet  14 , a coil  30 , a yoke  20 , and attracted means  19  composed of a plurality of attracted pieces  18  which are arranged radially around the rotation axis  12  and are magnetized by the permanent magnet  14 . The permanent magnet  14 , the coil  30 , the yoke  20 , and the attracted means  19  are mounted on the rotation axis  12  and the attracted pieces  18  that constitute the attracted means  19  are each placed in positions that correspond to positions that bisect the spaces between the metal pieces that constitute the yoke  20 , so that the cogging torque exerted on the rotation axis  12  is reduced.

FIELD OF THE INVENTION

The present invention relates to an electric generator. Moreparticularly, the invention relates to an electric generator thatdecreases effects exerted on a rotation axis by a so-called coggingtorque that is generated when magnetic field supplying means attracts ayoke.

BACKGROUND OF THE INVENTION

Based on the principle of operation, electric generators are categorizedinto synchronous generators, induction generators, and direct currentgenerators. In any of these generators, when a magnetic field is appliedto the coil of wire, an electromotive force is generated in the coil.

As a small synchronous generator, a bicycle dynamo is generally wellknown. In the bicycle dynamo, when a permanent magnet with south polesand north poles alternately arranged is turned, iron pieces provided tothe coil are magnetized and an electromotive force is generated in thecoil.

Such iron pieces provided to the coil are close to the permanent magnetat a small distance so as to efficiently apply a magnetic field to thecoil. If the permanent magnet with a strong magnetic force is used toapply a strong magnetic field to the coil, a strong attractive force ofthe permanent magnet to the iron pieces is generated between the ironpieces and the permanent magnet. The force that the attractive forceexerts on a rotation axis is called cogging torque. If the coggingtorque is strong, various problem such as running torque fluctuations,abnormal vibration, and noise arise. For example, in the case of abicycle dynamo, a heavy load is applied to the wheel when the wheel isturned. In the case of a wind turbine generator or the like, if coggingtorque is strong, starting torque of a rotor becomes strong. Inaddition, the resistance to continuous rotation of the rotor becomeshigh. For this reason, it is difficult to generate electricity in lightwind conditions.

DISCLOSURE OF THE INVENTION

An electric generator of the present invention comprises: a permanentmagnet composed of magnetic poles arranged radially and alternatelyaround a rotation axis; a coil wound around an electrically insulatedbobbin; a plurality of metal pieces that rotate relatively to thepermanent magnet and that apply magnetic flux generated by the permanentmagnet to the coil; and attracted means having a plurality of attractedpieces that are arranged radially around the rotation axis and that aremagnetized by the permanent magnet, wherein the attracted pieces of theattracted means are placed in such positions that they do not correspondto the metal pieces.

Further, an electric generator of the present invention comprises: apermanent magnet composed of magnetic poles arranged radially andalternately around a rotation axis; a coil wound around an electricallyinsulated bobbin; a plurality of metal pieces that rotate relatively tothe permanent magnet and that apply magnetic flux generated by thepermanent magnet to the coil; and attracted means having a plurality ofattracted pieces that are arranged radially around the rotation axis andthat are magnetized by the permanent magnet, wherein the attractedpieces of the attracted means are placed in positions that correspond topositions that bisect spaces between the metal pieces.

Further, an electric generator of the present invention comprises: apermanent magnet composed of magnetic poles arranged radially andalternately around a rotation axis; and two wire wound means composed ofa coil wound around an electrically insulated bobbin and a plurality ofmetal pieces that rotate relatively to the permanent magnet and thatapply magnetic flux generated by the permanent magnet to the coil,wherein the metal pieces of one of the wire wound means are placed insuch positions that they do not correspond to the metal pieces of theother wire wound means.

Further, an electric generator of the present invention comprises: apermanent magnet composed of magnetic poles arranged radially andalternately around a rotation axis; and two wire wound means composed ofa coil wound around an electrically insulated bobbin and a plurality ofmetal pieces that rotate relatively to the permanent magnet and thatapply magnetic flux generated by the permanent magnet to the coil,wherein the metal pieces of one of the wire wound means are placed inpositions that correspond to positions that bisect spaces between themetal pieces of the other wire wound means.

Further, an electric generator of the present invention comprises aplurality of electric generating means having a permanent magnetcomposed of magnetic poles arranged radially and alternately around arotation axis, a coil wound around an electrically insulated bobbin, anda plurality of metal pieces that rotate relatively to the permanentmagnet and that apply magnetic flux generated by the permanent magnet tothe coil, wherein the metal pieces of any one of the electric generatingmeans are placed in such positions that they do not correspond to themetal pieces of the rest of the electric generating means.

Further, an electric generator of the present invention comprises aplurality of electric generating means having a permanent magnetcomposed of magnetic poles arranged radially and alternately around arotation axis, a coil wound around an electrically insulated bobbin, anda plurality of metal pieces that rotate relatively to the permanentmagnet and that apply magnetic flux generated by the permanent magnet tothe coil, wherein the metal pieces of any one of the electric generatingmeans are placed in positions that correspond to positions that bisectspaces between the respective metal pieces of the rest of the electricgenerating means.

Further, an electric generator of the present invention comprises aplurality of electric generating means having a permanent magnetcomposed of magnetic poles arranged radially and alternately around arotation axis, a coil wound around an electrically insulated bobbin, anda plurality of metal pieces that rotate relatively to the permanentmagnet and that apply magnetic flux generated by the permanent magnet tothe coil, wherein the magnetic poles of any one of the electricgenerating means are placed in such positions that they do notcorrespond to the magnetic poles of the rest of the electric generatingmeans.

Further, an electric generator of the present invention comprises aplurality of electric generating means having a permanent magnetcomposed of magnetic poles arranged radially and alternately around arotation axis, a coil wound around an electrically insulated bobbin, anda plurality of metal pieces that rotate relatively to the permanentmagnet and that apply magnetic flux generated by the permanent magnet tothe coil, wherein the magnetic poles of any one of the electricgenerating means are placed in positions that correspond to positionsthat bisect spaces between the magnetic poles of the rest of theelectric generating means.

Further, in the electric generator of the present invention, theaforementioned permanent magnet is a cylindrical-shaped permanent magnetcomposed of magnetic poles arranged radially and alternately around therotation axis, and the aforementioned plurality of metal pieces and theaforementioned attracted pieces of the attracted means are close to theouter perimeter of the permanent magnet.

Further, in the electric generator of the present invention, theaforementioned permanent magnet is a cylindrical-shaped permanent magnetcomposed of magnetic poles arranged radially and alternately around therotation axis, and the aforementioned plurality of metal pieces areclose to the outer perimeter of the permanent magnet.

Further, in the electric generator of the present invention, theaforementioned permanent magnet is a ring-shaped permanent magnetcomposed of magnetic poles arranged radially and alternately around therotation axis, and the aforementioned plurality of metal pieces and theaforementioned attracted pieces of the attracted means are close to theinside perimeter of the permanent magnet.

Further, in the electric generator of the present invention, theaforementioned permanent magnet is a ring-shaped permanent magnetcomposed of magnetic poles arranged radially and alternately around therotation axis, and the aforementioned plurality of metal pieces areclose to the inside perimeter of the permanent magnet.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of an electric generator according to afirst embodiment of the present invention.

FIG. 2 is an exploded perspective view of an electric generatoraccording to the first embodiment of the present invention.

FIG. 3 is a perspective view of a first yoke and a second yoke thatconstitute a yoke 20 according to the first embodiment of the presentinvention.

FIGS. 4(a) to 4(d) are sectional views showing a positional relationshipbetween field iron piece, permanent magnet, and attracted pieces in theelectric generator according to the first embodiment of the presentinvention, and schematically illustrate the changes in distances betweena magnetic field of the permanent magnet, field iron pieces, andattracted pieces during the rotation of rotational axis.

FIG. 5 is a cross-sectional schematic view of an electric generatoraccording to a second embodiment of the present invention.

FIG. 6 is a cross-sectional schematic view of an electric generatoraccording to a third embodiment of the present invention.

FIG. 7 is a perspective view of an electric generator according to afourth embodiment of the present invention.

FIGS. 8(a) and 8(b) are sectional views showing a positionalrelationship between field iron pieces in the electric generatoraccording to the fourth embodiment of the present invention.

FIGS. 9(a) to 9(c) are sectional views illustrating the changes of thepositional relationship between field iron pieces and magnetic poles ofthe permanent magnet during the rotation of the rotational axis in theelectric generator according to the fourth embodiment of the presentinvention. In FIGS. 9(a) to 9(c), an upper view is a sectional viewtaken on line A-A of FIG. 7 and a lower view is a sectional view takenon line B-B of FIG. 7.

FIG. 10 is an exploded perspective view of the electric generatoraccording to a fifth embodiment of the present invention.

FIG. 11 is a sectional view of an electric generator according to thefifth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described withreference to the accompanying drawings. FIG. 1 is a perspective view ofan electric generator 10 according to the first embodiment and FIG. 2 isan exploded perspective view of the electric generator 10. The electricgenerator 10 comprises: a permanent magnet 14 with magnetic polesarranged radially and alternately around a rotation axis 12 to whichrotational power is transmitted from the outside; a coil 30 wound aroundan electrically insulated bobbin 31; a yoke 20 for applying magneticflux generated by the permanent magnet 14 to the coil 30; and attractedmeans 19 having a plurality of attracted pieces 18 that are magnetizedby the permanent magnet 14 and that are arranged radially around therotation axis 12. In FIG. 1, an arrow R indicates a rotational directionof the rotation axis.

In this embodiment, the yoke 20, the coil 30, and the attracted means 19are a stator, and the permanent magnet 14 is a rotator. However, thepermanent magnet 14 may be used as a stator while the yoke 20, the coil30, and the attracted means 19 may be used as a rotator.

First, the permanent magnet 14 will be described. As shown in FIG. 2,the permanent magnet 14 is shaped like a disk having a proper thicknessand the center of the permanent magnet is fixed by the rotation axis 12.In this permanent magnet 14, 45 degree pie-shaped north poles and southpoles are arranged alternately around the rotation axis 12. Thisdisk-shaped permanent magnet 14 has opposite magnetic poles on itsreverse side in the thickness direction.

In this permanent magnet 14, volumes and magnetic flux densities of therespective magnetic poles are equal. In this embodiment, the permanentmagnet 14 is made of ferrite. In this permanent magnet 14, one of theside surface close to the yoke 20 is hereinafter referred to as “frontsurface” and the other side surface close to the attracted means 19 isreferred to as “back surface”.

While the disk-shaped permanent magnet 14 is used in this embodiment,the shape of the permanent magnet is not particularly limited as far asthe magnetic poles are arranged radially around the rotation axis 12.For example, independent rectangular permanent magnets may be arrangedradially around the rotation axis 12.

In the permanent magnet 14, the magnetic flux density is deemed to bethe highest at the center of the surface of each magnetic pole.Therefore, when the position of the permanent magnet 14 will bedescribed, the position of the center of the surface of the pole is usedas a pitch reference. Also, when the positions of the field iron piece26 and the attracted piece 18 will be described later, a pitch linepassing the center of the respective pieces 26 and 18 and extendingradially around the rotation axis 12 is used as a reference.

Next, the yoke 20 will be described with reference to FIG. 3. FIG. 3 isa perspective view of a first yoke 20 a and a second yoke 20 b thatconstitute the yoke 20. In the first yoke 20 a, four long plates 22 aare joined to a peripheral portion 22 b around the rotation axis 12, andan end of each long plate 22 a is bent into an L shape to form a firstiron piece 22. The first iron pieces 22 are close to and parallel to thefront surface of the permanent magnet 14. The distance between thepermanent magnet 14 and the first iron pieces 22 is about 2 millimeters.The four long plates 22 a are developed radially around the rotationaxis 12 at a pitch angle of 90 degrees and cover the coil 30 from theoutside. Therefore, the first iron pieces 22 are placed at a pitch angleof 90 degrees around the rotation axis 12.

In the second yoke 20 b, four short plates 24 a are combined together ina hollow portion of the bobbin 31 (a portion through which the rotationaxis 12 passes) and an end of each short plate 24 a is bent into an Lshape to form a second iron piece 24. The second iron pieces 24 areclose to and parallel to the front surface of the permanent magnet 14.The four short plates 24 a are developed radially around the rotationaxis 12 at a pitch angle of 90 degrees. In other words, the second ironpieces 24 are placed at a pitch angle of 90 degrees around the rotationaxis 12.

The first iron pieces 22 and the second iron pieces 24 are joinedtogether and placed at 45 degrees apart from each other around therotation axis 12. Further, the first iron pieces 22 and the second ironpieces 24 are rotatably mounted on the rotation axis 12 through abearing 66. In this embodiment, the first iron pieces 22 and the secondiron pieces 24 are rectangular in shape. However, in order that largerareas of the first iron pieces 22 and the second iron pieces 24 can beclose to the permanent magnet 14, they may be substantially fan-shaped.The first iron pieces 22 and the second iron pieces 24 are hereinafterreferred to as “field iron piece 26”, unless specified otherwise. Inthis embodiment, the field iron piece 26 is formed of silicon steelplate.

Next, the coil 30 will be described with reference to FIG. 1. The coil30 is formed by winding a copper wire on a ring-shaped bobbin 31 that iselectrically insulated since it is made of synthetic resin. The firstyoke 20 a and the second yoke 20 b are fixed to the coil 30 through thebearing 66 to form a stator. The stator is mounted on the rotation axis12 in such a manner that the rotation axis 12 can be freely rotated.

Next, the attracted means 19 will be described with reference to FIG. 2.The attracted means 19 is composed of a fixed base 36 and eightattracted pieces 18. As shown in FIG. 2, on the back side of thepermanent magnet 14, a disk-shaped fixed base 36 having a properthickness is supported by the rotation axis 12 that passes through thecenter of the base 36. Since this fixed base 36 is formed ofnon-magnetic material, it is not magnetized by the permanent magnet 14.In this embodiment, the fixed base is formed of synthetic resin.

On the permanent magnet's side of the fixed base 36, eight rectangularattracted pieces 18 formed of the same material as the field iron pieces26 are provided. The attracted pieces 18 are fixed to the positions onthe base 36 that correspond to the positions that bisect the spacesbetween the field iron pieces 26 and are arranged radially around therotation axis 12. The fixed base 36 is fixed to the rotation axis 12through the bearing 66. Therefore, the base 36 is freely rotatablearound the rotation axis 12.

The distance between the permanent magnet 14 and the attracted pieces 18is the same as that between the field iron pieces 26 and the permanentmagnet 14. For example, it is about 2 millimeters in this embodiment.Further, the area of the attracted piece 18 is the same as that of thefield iron piece 26. Further, it is preferable that the shape and thearea of the attracted piece 18 is the same as those of the field ironpiece 26.

Next, a positional relationship between the field iron pieces 26 and theattracted pieces 18 will be described with reference to FIG. 2. Theeight field iron pieces 26 are spaced equally at an angle pitch of 45degrees around the rotation axis 12. Also, the eight attracted pieces 18are spaced equally at an angle pitch of 45 degrees around thecircumference that is divided into eight about the rotation axis 12. Theeight field iron pieces 26 and the eight attracted pieces 18 arestaggered at an angle of 22.5 degrees that is half of 45 degrees.

The stator in which the yoke 20 and the coil 30 are integrally formedand the fixed base 36 having the attracted pieces thereon are fixed to acase (not shown) that covers the electric generator 10. Therefore, thepositions of the field iron pieces 26 and the attracted pieces 18 areplaced at a fixed position in such a manner they are staggered at 22.5degrees.

A function of this embodiment will be described below. In this electricgenerator 10, magnetic flux applied to the field iron pieces 26 by thepermanent magnet 14 crosses the coil 30 in the axial direction andthereby the coil 30 produces an electromagnetic force. When thepermanent magnet 1 rotates with the rotation axis 12, the magnetic polesapplied to the field iron pieces 26 are reversed alternately. Byalternately reversing the direction of the magnetic flux crossing thecoil 30 in the axial direction, the coil 30 produces the electromagneticforce continuously.

FIGS. 4(a) to 4(d) are a schematic cross sectional view of the electricgenerator 10 of the first embodiment. The permanent magnet 14 rotateswith the field iron pieces 26 and the attracted pieces 18 fixed. Thepermanent magnet 14 rotates in the direction of an arrow R shown inFIG. 1. In FIGS. 4(a) to 4(d), the rotation of the permanent magnet 14is shown by a down to up movement.

FIG. 4(a) shows that the permanent magnet 14 exerts a strong attractiveforce on the field iron pieces 26. FIG. 4(b) shows the state after thepermanent magnet 14 rotated 11.25 degrees (half of the 22.5 degrees)about the rotation axis 12 from the state shown in FIG. 4(a). FIG. 4(c)shows that the state after the permanent magnet 14 rotated 11.25 degreesabout the rotation axis 12 from the state shown in FIG. 4(b). FIG. 4(d)shows that the state after the permanent magnet 14 rotated 11.25 degreesabout the rotation axis 12 from the state shown in FIG. 4(c). Apositional relationship between the permanent magnet 14 shadowed in FIG.4(a) to 4(d) and the field iron pieces 16 or the attracted pieces 18will be described below.

In FIG. 4(a), when a span between the field iron pieces 26 is d, a spanbetween the field iron piece 26 and the attracted piece 18 is d/2. Whenthe permanent magnet 14 is in a position shown in FIG. 4(a), a distancebetween the permanent magnet 14 and the attracted pieces 18 is u and adistance between the permanent magnet 14 and the field iron pieces 26 ist. When the permanent magnet 14 is in a position shown in FIG. 4(b), adistance between the permanent magnet 14 and the field iron pieces 26and a distance between the permanent magnet 14 and the attracted pieces18 are r. Among the distances t, u, and r, the distance t is theshortest and the distance u is the longest.

In the state shown in FIG. 4(a), since there is a distance of t betweenthe field iron pieces 26 and the north pole of the permanent magnet 14,the south pole that is an opposite magnetic pole appears remarkably inthe field iron piece 26. Further, since there is a distance of u betweenthe south pole of the permanent magnet 14 and the attracted pieces 18,the north pole that is an opposite magnetic pole appears weakly in theattracted pieces 18 placed on the both sides of the permanent magnet 14.

In the state shown in FIG. 4(b), since there is a distance of r betweenthe field iron pieces 26 and the north pole of the permanent magnet 14,the south pole that is an opposite magnetic pole appears weakly in oneof the field iron pieces 26. Further, since there is a distance of rbetween the attracted piece 18 and the south pole of the permanentmagnet 14, the north pole that is an opposite magnetic pole appearsweakly in one of the attracted pieces 18. In this state, the attractiveforce that the permanent magnet 14 exerts on the field iron pieces 26 isbalanced with the attractive force that the permanent magnet 14 exertson the attracted pieces 18.

In the state shown in FIG. 4(c), since there is a distance of u betweenthe permanent magnet 14 and the field iron pieces 26, the south polethat is an opposite magnetic pole appears weakly in the field ironpieces 26 placed on the both sides of the north pole of the permanentmagnet 14. Further, since there is a distance of t between the attractedpieces 18 and the south pole of the permanent magnet 14, the north polethat is an opposite magnetic pole appears remarkably in the field ironpiece 26.

In the state shown in FIG. 4(d), since there is a distance of r betweenthe field iron pieces 26 and the north pole of the permanent magnet 14,the south pole that is an opposite magnetic pole appears weakly in oneof the field iron piece 26. Further, since there is a distance of rbetween the attracted pieces 18 and the south pole of the permanentmagnet 14, the north pole that is an opposite magnetic pole appearsweakly in one of the attracted pieces 18. In this state, the attractiveforce that the permanent magnet 14 exerts on the field iron pieces 26 isbalanced with the attractive force that the permanent magnet 14 exertson the attracted pieces 18.

Next, an attractive force exerted on the rotation axis 12 during thetransition from the state shown in FIG. 4(a) to that shown in FIG. 4(b)will be described below. When the rotation axis 12 rotates even slightlyfrom the position where the permanent magnet 14 exerts a strongattractive force on the field iron pieces 26, the attractive force thatthe permanent magnet 14 exerts on the field iron pieces 26 decreaseswhile the attractive force that the permanent magnet 14 exerts on theattracted pieces 18 increases. In this case, when the permanent magnet14 rotates slightly form the position where the permanent magnet 14exerts the strongest attractive force on the field iron pieces 26,forces are exerted in a direction that the north pole generated on theattracted pieces 18 attracts the south pole of the permanent magnet 14.This cancels the attractive force that the north pole of the permanentmagnet 14 exerts on the field iron pieces 26 to some extent andtherefore the attractive force exerted on the rotation axis 12, namelycogging torque, decreases. In other words, although the maximum value ofthe cogging torque exerted on the rotation axis 12 does not decrease,the attractive force exerted on the field iron pieces 26 by thepermanent magnet 14, which hinders the rotation of the rotation axis 12,can be decreased by exerting the attractive force in a direction thatthe field iron pieces 26 attract the permanent magnet 14. Therefore, thetime that the field iron pieces 26 strongly attract the permanent magnet14 can be shortened.

Next, an attractive force exerted on the rotation axis 12 during thetransition from the state shown in FIG. 4(b) to that shown in FIG. 4(c)will be described below. When the rotation axis 12 rotates even slightlyfrom the position where the permanent magnet 14 is between the fieldiron piece 16 and the attracted piece 18, the distance between thepermanent magnet 14 and the attracted pieces 18 becomes shorter so thatthe attractive force exerted in the direction that the permanent magnet14 attracts the attracted portion 18 increases. As this result, thedistance between the permanent magnet 14 and the field iron pieces 26becomes longer and the attractive force exerted in the direction thatthe permanent magnet 14 attracts the field iron pieces 26 becomesweaker.

Next, an attractive force exerted on the rotation axis 12 during thetransition from the state shown in FIG. 4(c) to that shown in FIG. 4(d)will be described below. When the rotation axis 12 rotates even slightlyfrom the position where the permanent magnet 14 exerts a strongattractive force on the attracted pieces 18, the attractive force thatthe permanent magnet 14 exerts on the field iron pieces 26 increaseswhile the attractive force, which the permanent magnet 14 exerts on theattracted pieces 18, decreases. In this case, when the permanent magnet14 rotates slightly form the position where the permanent magnet 14exerts the strongest attractive force on the attracted pieces 18, forcesare exerted in a direction that the south pole generated on the fieldiron piece 26 attracts the north pole of the permanent magnet 14. Thiscancels the attractive force that the south pole of the permanent magnet14 exerts on the attracted pieces 18 to some extent and therefore theattractive force exerted on the rotation axis 12, namely cogging torque,decreases.

Next, an attractive force exerted on the rotation axis 12 during thetransition from the state shown in FIG. 4(d) to that shown in FIG. 4(a)will be described below. When the rotation axis 12 rotates even slightlyfrom the position where the permanent magnet 14 is between the fieldiron piece 16 and the attracted piece 18, the distance between thepermanent magnet 14 and the field iron piece 26 becomes shorter so thatthe attractive force exerted in the direction that the permanent magnet14 attracts the field-iron piece 26 increases. As this result, thedistance between the permanent magnet 14 and the attracted piecesbecomes longer and the attractive force exerted in the direction thatthe permanent magnet 14 attracts the attracted pieces 18 becomes weaker.

Compared to the case where there are no attracted pieces 18, coggingtorque is generated in more positions in the case where there are theattracted pieces 18. However, the maximum value of the cogging torque inthe direction where the rotation of the rotation axis 12 is hindereddoes not change, but the positions where the cogging torque is generatedbecomes double. In other words, compared to the case where there are noattracted pieces 18, a cycle of the cogging torque is halved.

During the transition from the state shown in FIG. 4(a) to that shown inFIG. 4(b), the attracted pieces 18 placed between the field iron pieces26 positively attract the permanent magnet 14 and thereby an attractiveforce between the permanent magnet 14 and the field iron pieces 26 isreduced. Alternatively, during the transition from the state shown inFIG. 4(c) to that shown in FIG. 4(d), the field iron pieces 26 placed inpositions that correspond to positions between the attracted pieces 18positively attract the permanent magnet 14 and thereby an attractiveforce between the permanent magnet 14 and the attracted pieces 18 isreduced.

Accordingly, the maximum value of the cogging torque exerted on therotation axis 12 does not change, but the cogging torque is exerted onthe rotation axis 12 only for a short time and the cycle of the coggingtorque is halved. This allows a smooth rotation of the rotation axis 12.

In the first embodiment, the permanent magnet 14 having eight magneticpoles is used. However, a permanent magnet having more magnetic polescan be used within an acceptable range for design. The numbers of thefield iron pieces 26 and the attracted pieces 18 are also increased sothat they are as many as the magnetic poles of the permanent magnet 14.

Further, in the first embodiment, the attracted pieces 18 are providedon the back side of the permanent magnet 14. However, a different yokefor applying magnetic flux to a coil may be used instead of theattracted pieces 18.

Next, a second embodiment in which a different yoke for applyingmagnetic flux to a coil instead of the attracted pieces 18 will bedescribed. In the second embodiment, a disk-like permanent magnet 14 ismounted on one rotation axis 12 and wire wound means 17 a and 17 b areprovided on both sides of the disk-like permanent magnet 14 in such amanner that the wire wound means 17 a and 17 b are opposed to eachother, as shown in FIG. 5. The wire wound means 17 a is composed of thefield iron pieces 26 a and the coil 30 a and the wire wound means 17 bis composed of the field iron pieces 26 b and the coil 30 b. The wirewound means 17 a and 17 b are of the same structure. The field ironpieces 26 b of the wire wound means 17 b are placed in such positionsthat spaces between the field iron pieces 26 a of the wire wound means17 a are divided into equal halves. The permanent magnet 14, the fieldiron pieces 26 a and 26 b, and the coil 30 a and 30 b are of the samestructure as those described in the first embodiment.

Specifically, as shown in FIG. 5, the field iron pieces 26 a of the wirewound means 17 a are staggered at 22.5 degrees apart from the field ironpieces 26 b of the wire wound means 17 b. This is the same positionalrelationship as that between the field iron pieces 26 and the attractedpieces 18 of the electric generator 10 according to the firstembodiment.

Thus, in the same manner as the first embodiment, the cycle of thecogging torque is halved. When the rotation axis 12 rotates evenslightly from the position where the maximum cogging torque is exerted,the field iron pieces 26 attract the permanent magnet 14. This inducesthe rotation of the rotation axis 12 and allows a smooth rotation of therotation axis 12.

Next, there will be described a synthesized voltage of the coil 30 a and30 b where the field iron pieces 26 a and 26 b are staggered at 22.5degrees from each other. When the coil 30 a and the coil 30 b areconnected in series, sine waves whose phases are shifted are synthesizedand thus a synthesized voltage is produced. In the second embodiment,the permanent magnet has eight magnetic poles. When the permanent magnet14 makes a turn, four cycles of voltage are output to the coils 30 a and30 b. However, a voltage output from the coil 30 a is an electric angleof 90 degrees out of phase with a voltage output from the coil 30 b.Accordingly, the maximum value of the synthesized voltage is the squareroot of 2 times the voltage generated by the coil 30. In the secondembodiment, the field iron pieces 26 b are placed in such positions thatthe field iron pieces 26 a are divided into two halves. This is underthe same technical concept as the placement of the field iron pieces 26a and 26 b staggered at an electrical angle of 90 degrees from eachother, in the case of eight magnetic poles. Specifically, in the case ofeight magnetic poles, “to be staggered at a mechanical angle of 22.5degrees” is the same meaning as “to be staggered at an electric angle of90 degrees”.

In the second embodiment, two wire wound means 17 a and 17 b share thepermanent magnet 14. This allows a smooth rotation of the rotation axis12 without increasing the maximum value of the cogging torque. In thiscase, when the two wire wound means 17 a and 17 b are connected inseries, the voltage value also becomes the square root of 2 times the=voltage of a single wire wound means. In other words, compared to thecase where a single wire wound means is used, the rotation axis 12 isturned by the same force but the maximum voltage can be increased thesquare root of 2 times. In this case, the moment of inertia applied tothe rotation axis 12 is not considered.

Further, in the second embodiment, the disk-like permanent magnet 14 ismounted on the single rotation axis 12 and the wire wound means 17 a and17 b are provided on the both sides of the permanent magnet 14, but thenumbers of wire wound means 17 and the permanent magnet 14 are notlimited thereto. The scope of the present invention covers an electricgenerator in which a plurality of permanent magnets 14 are mounted on asingle rotation axis 12 and two wire wound means 17 are provided to theboth sides of each permanent magnet 14.

Where a plurality of wire wound means 17 are provided, it is desirablethat the field iron pieces are so placed that the phase of thesynthesized voltage of the plurality of wire wound means 17 connected inseries is 90 degrees out of phase with the voltage of a single wirewound means. In other words, in the case where four wire wound means 14are mounted on a single rotation axis 12, it is desirable that the fieldiron pieces 26 of the respective wire wound means 17 are spaced equallyand staggered at 15 degrees apart from each other. In this case, it ispremised that the two permanent magnets 14 have magnetic poles on thesame positions.

A third embodiment of the present invention will be described withreference to FIG. 6. FIG. 6 is a schematic sectional view of an electricgenerator 10 according to a third embodiment of the present invention.In the third embodiment, there will be described an electric generator10 in which two sets of electromotive means 16 (a combination of coils30, field iron pieces 26, permanent magnets 14, attracted pieces 18, andfixed bases 36) are mounted on the rotation axis 12 and in which therotation axis 12 is smoothly rotated. In FIG. 6, on the left side iselectromotive means 16 a and on the right side is electromotive means 16b.

When the two sets of electromotive means 16 a and 16 b are mounted onthe rotation axis 12, if the field iron pieces 26 and the permanentmagnets 14 of the electromotive means 16 a and 16 b are placedsymmetrically with respect to the rotation axis 12, the maximum value ofthe cogging torque becomes double. This value is calculated withoutconsideration of frictional resistance and the like.

In the third embodiment, when the two sets of electromotive means 16 aand 16 b are mounted on the rotation axis 12, the permanent magnets 14in the electromotive means 16 a are placed in such positions that thecogging torque becomes minimum while the permanent magnets 14 in theelectromotive means 16 b are placed in such positions that the coggingtorque becomes maximum.

In the left electromotive means 16 a shown in FIG. 6, the permanentmagnet 14 is at the midpoint (d/4) of the span d/2 between the fieldiron piece 26 and the attracted piece 18. This position is a positionwhere the cogging torque becomes minimum in the electromotive means 16a. On the other hand, in the right electromotive means 16 b shown inFIG. 6, the permanent magnet 14 is placed in a position closest to thefield iron piece 26. This position is a position where the coggingtorque becomes maximum in the electromotive means 16 b.

Specifically, in the two sets of electromotive means 16 a and 16 b, thefield iron pieces 26 and the attracted pieces 18 are placedsymmetrically with respect to the fixed bases 36. In the one set ofelectromotive means, the respective permanent magnets 14 are placed insuch positions that the minimum cogging torque is generated, and in theother set of electromotive means, the respective permanent magnets 14are placed in such positions that the maximum cogging torque isgenerated. Thus the electromotive means are mounted on the rotation axis12 in such a manner that the permanent magnets 14 in both electromotivemeans are staggered.

In the third embodiment, the maximum cogging torque is generated atdifferent positions in the two electromotive means 16 a and 16 b.Therefore, compared to the case where the two sets of electromotivemeans 16 a and 16 b are placed symmetrically (the field magnetic pieces26, attracted pieces 18, and the permanent magnets 14 are placedsymmetrically with respect to the fixed stage 36), the maxim value ofthe cogging torque that is generated when the two sets of electromotivemeans 16 are turned at the same time can be reduced. Further, comparedto the case where the two sets of electromotive means 16 a and 16 b areplaced symmetrically, the cycle of the maximum cogging torque that isgenerated when the rotation axis is turned is halved.

Further, in the third embodiment, the electromotive means 16 a and 16 bare mounted on the rotation axis 12 in such a manner that the permanentmagnets 14 are placed in such positions that the cogging torque ismaximum in the electromotive means 16 a while the permanent magnets 14are placed in such positions that the cogging torque is minimum in theelectromotive means 16 b. This is the same relationship as that betweenthe field iron pieces 26 and the attracted pieces 18 in the firstembodiment. Specifically, when the electromagnetic means 16 a rotateseven slightly from the position where the maximum cogging torque isgenerated, the other electromagnetic means 16 b generates the attractiveforce, which decreases the attractive force exerted on the rotation axis12 by the electromotive means 16 a. Accordingly, the cogging torque isexerted on the rotation axis 12 only for a short time and the cycle ofthe cogging torque is halved. This allows a smooth rotation of therotation axis 12.

While it has been described in the third embodiment that the two sets ofelectromotive means 16 are mounted on the same rotation axis 12, thenumber of electromotive means 16 are not limited to two sets. In thecase where three or more sets of the electromotive means 16 are mountedon the rotation axis 12, it is sufficient to mount them in such a mannerthat the position where the maximum cogging torque is generated variesdepending on the respective electromotive means. As a method of mountingthe electromotive means in such a manner that the position where themaximum cogging torque is generated varies depending on the respectiveelectromotive means, there may be employed a method of staggering thepermanent magnets 14 or a method of staggering the field iron pieces 26,as described in the third embodiment.

Further, if a plurality of the electromotive means 16 are provided inthe third embodiment, it is desirable that the electromotive means 16are so positioned that the phase of the synthesized voltage of theelectromotive means 16 connected in series is electric angle of 45degrees out of phase with that of the voltage of a single electromotivemeans 16.

A fourth embodiment of the present invention will be described withreference to FIG. 7. FIG. 7 is a perspective view of an electricgenerator 10 according to the fourth embodiment of the presentinvention. In the fourth embodiment, there will be described an electricgenerator 10 in which two sets of electric generating means 28 a and 28b (a combination of permanent magnet, coil, and yoke) are mounted on therotation axis 12 and in which the rotation axis 12 is smoothly rotated.

This electric generator 10 comprises a rotation axis 12 to which torqueis transmitted by a force from outside, a first permanent magnet 40 anda second permanent magnet 42 that are field magnet means mounted on therotation axis 12, a first yoke 46 composed of eight iron pieces to whichmagnetic flux is applied by the first permanent magnet 40, a first coil32 to which magnetic flux is applied by the first yoke, a second yoke 46composed of eight iron pieces to which magnetic flux is applied by thesecond permanent magnet 42, and a second coil 34 to which magnetic fluxis applied by the second yoke 46.

The first permanent magnet 40 and the second permanent magnet 42 have acylindrical shape, and the first permanent magnet 40 and the secondpermanent magnet 42 are mounted on the rotation axis 12. On the firstpermanent magnet 40 and the second permanent magnet 42, eight polescomposed of north poles and south poles are staggered along the outerperiphery, respectively. In other words, magnetic poles that pair upwith the magnetic poles staggered along the outer periphery are providedon the inside surface of the rotation axis 12. Further, on the firstpermanent magnet 40 and the second permanent magnet 42, magnetic polesare so arranged that different magnetic poles are opposed to each other.However, the first permanent magnet 40 and the second permanent magnet42 are separated from each other by a non-magnetic panel (not shown) sothat they are not influenced from each other.

The first yoke 44 to which magnetic flux is applied by the firstpermanent 40 is composed of four plate-like first long iron pieces 48and four plate-like short iron pieces 50. The length of the first longiron-piece 48 is substantially equal to the axial length of the firstcoil 32 and the axial length of the first permanent magnet 40. Thelength of the first short iron piece 50 is substantially equal to theaxial length of the first permanent magnet 40.

The four long iron pieces 48 are like a long plate. One end of each longiron piece 48 is extended. The extended ends of the respective firstlong iron pieces 48 are joined together around the rotation axis 12. Thefirst long iron pieces 48 are in close vicinity to the outer surface ofthe first coil 32 and the outer surface of the first permanent magnet40. These four iron pieces are spaced at 90 degrees apart from eachother. Likewise, one end of each first short iron piece 50 is extended.The extended ends of the respective first short iron pieces 50 arejoined together around the rotation axis 12.

These first short iron pieces 50 are in close vicinity to the outersurface of the first permanent magnet 40 and the one end of each ironpiece 50 is in contact with the inside surface of the first coil 32.These four iron pieces are spaced at 90 degrees apart from each otheraround the rotation axis 12. These first long iron pieces 48 and firstshort iron pieces 50 are mounted rotatably on the rotation axis 12.

The first long iron pieces 48 and the first short iron pieces 50 arestaggered and arranged radially around the rotation axis 12. Therefore,the first long iron pieces 48 and the first short iron pieces 50 areplaced at 45 degrees apart from each other around the rotation axis 12.

As in the case of the first yoke 44, the second yoke 46 to whichmagnetic flux is appli ed by the second permanent magnet 42 is composedof four plate-like second long iron pieces 52 and four plate-like secondshort iron pieces 54. The second long iron pieces 52 and the secondshort iron pieces 54 are of the same structure as those of the firstyoke 44.

Next, the positional relationship between the first yoke 44 and thesecond yoke 46 will be described. The first long iron pieces 48 and thefirst short iron pieces 50 of the first yoke and the second long ironpieces 52 and the second short iron pieces 54 of the second yoke 46 arestaggered around the rotation axis 12. For example, the first long ironpieces 48 of the first yoke 44 are placed at 22.5 degrees apart from thesecond long iron pieces 52 of the second yoke 46 around the rotationaxis 12. This positional relationship is the same as the positionalrelationship between the field iron pieces 26 and the attracted pieces18.

FIGS. 8(a) and 8(b) schematically show how the respective iron pieces ofthe first yoke 44 and the second yoke 46 are positioned around therotation axis 12. In FIG. 8(a), pitch lines are shown around therotation axis 12. Solid lines are pitch lines of the iron piecesconstituting the first yoke 44, and doted lines are pitch lines of theiron pieces constituting the second yoke 46. FIG. 8(b) showsschematically a cross section of the electric generator 10 of the fourthembodiment. The iron pieces of the first yoke 44 are placed at 45degrees apart from each other around the rotation axis 12. Further, theiron pieces of the first yoke 44 are placed at 22.5 degrees apart fromthe iron pieces of the second yoke 46.

A function of the fourth embodiment will be described. As shown in FIG.8(b), when the first long iron pieces 48 of the first yoke 44 becomesouth pole, the first short iron pieces 50 become north pole. In otherwords, magnetic lines of force flow from the first short iron pieces 50to first long iron pieces 48 to generate a magnetic field crossing thefirst coil 32 in the direction of the rotation axis 12.

FIGS. 9(a) to 9(c) are sectional views taken on line A-A of the electricgenerator 28 a and sectional views taken on line B-B of the electricgenerator 28 b. FIGS. 9(a) to 9(c) schematically show a positionalrelationship between the permanent magnet 14, the first yoke 44, and thesecond yoke 46 when the rotation axis 12 is turned in the direction ofan arrow R shown in FIG. 7. FIGS. 9(a) to 9(c) show a change inpositional relationship between the permanent magnet 14, the first yoke44, and the second yoke 46 during the rotation of the rotation axis 12.In the drawings, an upper view is a sectional view taken on line A-A anda lower view is a sectional view taken on line B-B.

In the upper sectional view taken on line A-A in FIG. 9(a), the ionpieces (first long iron piece 48 and first short iron piece 50)constituting the first yoke 44 are placed in positions where themagnetic flux density of the first permanent magnet 40 is maximum (infront of the centers of the north pole and the south pole). At thesepositions, a strong attractive force is exerted on the iron piecesconstituting the first yoke 44 and therefore strong cogging torque isgenerated on the rotation axis 12 on which the first permanent magnet 40is mounted.

On the other hand, the iron pieces (second long iron pieces 52 andsecond short iron pieces) constituting the second yoke 46 are placed infront of the borders between the magnetic poles of the second magneticpole 42 (borders between the north poles and the south poles), as shownin the lower sectional view taken on line B-B in FIG. 9(a). At theseplaces, only a weak attractive force is exerted on the iron pieces ofthe second yoke 46 and therefore weak cogging torque is generated on therotation axis 12 on which the second permanent magnet 42 is mounted.

When first permanent magnet 40 and the second permanent magnet 42mounted on the rotation axis 12 rotates about the rotation axis 12(rotation from the position shown in FIG. 9(a) to the position shown inFIG. 9(b)), the cogging torque exerted on the rotation axis 12 by thefirst permanent magnet 40 gradually becomes weak while the coggingtorque exerted on the rotation axis 12 by the second permanent magnet 42gradually becomes strong. Such states last until the respectivepermanent magnets move to the positions shown in FIG. 9(b).

As shown in the lower sectional view in FIG. 9(b) taken on line B-B, theiron pieces constituting the second yoke 46 are placed in the positionswhere the magnetic flux density of the second permanent magnet 42 ismaximum. At these positions, a strong attractive force is exerted on theiron pieces constituting the second yoke 46 and therefore strong coggingtorque is generated on the rotation axis 12 on which the secondpermanent magnet 42 is mounted. On the other hand, the iron piecesconstituting the first yoke 44 are placed in front of the bordersbetween the magnetic poles of the first permanent magnet 40. At thesepositions, only a weak attractive force is exerted on the iron pieces ofthe first yoke 44 and therefore weak cogging torque is generated on therotation axis 12 on which the first permanent magnet 40 is mounted.

The strength of the cogging torque is determined by the attractive forceof the permanent magnet for the iron pieces. In other words, strongattractive force for the iron pieces means strong cogging torque, whileweak attractive force for the iron pieces means weak cogging torque.

The attractive force exerted on the first permanent magnet 40 isweakened by the attractive force exerted on the second permanent magnet42 mounted on the rotation axis 12. Accordingly, the maximum value ofthe cogging torque exerted on the rotation axis 12 becomes smaller thanthe case where two electric generators are placed symmetrically.

When the first permanent magnet 40 and the second permanent magnet 42mounted on the rotation axis 12 further rotate (rotation from theposition shown in FIG. 9(b) to the position shown in FIG. 9(c)), theattractive force exerted on the second permanent magnet 42 graduallydecreases while the attractive force exerted on the first permanentmagnet 40 gradually increases. Such states last until the respectivepermanent magnets move to the positions shown in FIG. 9(c). In thiscase, the attractive force exerted on the second permanent magnet 42 isweakened by the attractive force exerted on the first permanent magnet40 mounted on the rotation axis 12. Accordingly, the maximum value ofthe cogging torque exerted on the rotation axis 12 becomes smaller thanthe case where two electric generators are placed symmetrically.

In the fourth embodiment, the positions where the maximum cogging torqueis generated are different depending on the electric generating means 28a and 28 b. Therefore, the maximum value of the cogging torque that isgenerated when the two electric generating means 28 are simultaneouslyturned can be less than the case where the two electric generating means28 a and 28 b are placed symmetrically. Further, when the rotation axis12 is turned, the cycle of the maximum cogging torque is half as long asthe case where the generating means 28 a and 28 b are placedsymmetrically.

Furthermore, in the fourth embodiment, the first yoke 44 is sopositioned that the cogging torque of the electric generating means 28 abecomes maximum, while the second yoke 46 is so positioned that thecogging torque of the electric generating means 28 b becomes minimum.Thus, the first yoke 44 and the second yoke 26 are mounted on therotation axis 12. The relationship between the first yoke and the secondyoke is the same as that between the field iron pieces 26 and theattracted pieces 18 described in the first embodiment. Specifically,when the rotation axis rotates even slightly from the position where thecogging torque of the electric generating means 28 a becomes maximum,the electric generating means 28 b generates the attractive force. Thisdecreases the attractive force exerted on the rotation axis 12 by theelectric generating means 28 a. Accordingly, the cogging torque isexerted on the rotation axis 12 only for a short time and the cycle ofthe cogging torque is halved. This allows a smooth rotation of therotation axis 12.

While it has been described in the fourth embodiment that the two setsof electric generating means 28 are mounted on the same rotation axis12, the number of electric generating means 28 are not limited to twosets. Where three or more sets of the electric generating means 28 aremounted on the rotation axis 12, it is sufficient to mount them in sucha manner that the position where the maximum cogging torque is generatedvaries depending on the respective electric generating means. As amethod of coupling the electric generating means in such a manner thatthe position where the maximum cogging torque is generated variesdepending on the respective electric generating means, there may beemployed a method of staggering the yokes or a method of staggering thepermanent magnets, as described in the fourth embodiment.

Further, if a plurality of the electric generating means 28 are providedin the fourth embodiment, it is desirable that the electric generatingmeans 28 are so positioned that the phase of the synthesized voltage ofthe electric generating means 28 connected in series is electric angleof 45 degrees out of phase with that of the voltage of a single electricgenerating means.

FIG. 10 shows a fifth embodiment of the electric generator 10 accordingto the present invention. FIG. 11 is a sectional view of the electricgenerator 10 according to the fifth embodiment. The electric generator10 according to the fifth embodiment comprises: a first coil 56 and asecond coil 58 mounted on the rotation axis 12; a first yoke 66 and asecond yoke 68 composed of a plurality of iron pieces provided to theouter peripheries of the first coil 56 and the second coil 58, andpermanent magnets 64 surrounding the first yoke 66 and the second yoke68. A combination of the first coil 56 and the first yoke 66 and acombination of the second coil 58 and the second yoke 68 are mounted onthe rotation axis 12.

The first coil 56 and the second coil 58 mounted on the rotation axis 12are formed by winding copper wire around a cylindrical bobbin (notshown) made of synthetic resin. The first coil 56 and the second coil 58are mounted on the rotation axis 12 that goes through the middle of thebobbin. Therefore, by turning the rotation axis 12, the first coil 56and the second coil 58 are turned.

The first yoke 66 provided to the outer periphery of the first coil 56is composed of fourteen first iron pieces 60 which are spaced equallyand radially about the rotation axis 12 and fourteen second iron pieces62 which are spaced equally and radially about the rotation axis 12.These twenty-eight iron pieces are about as long as the axial thicknessof the first coil 56. The fourteen first iron pieces 60 are so arrangedthat they surround the first coil 56 and are mounted on the rotationaxis 12.

Further, the fourteen second iron pieces 62 are arranged alternatelywith the fourteen first iron pieces 60 so that they surround the firstcoil 56 and are mounted on the rotation axis 12. In other words, thefirst coil 56 is surrounded by the first iron pieces 60 and the secondiron pieces 62.

As in the case of the first coil 56, the second coil 58 is alsosurrounded by twenty-eight iron pieces 60 and 62. The fourteen firstiron pieces 60 are spaced at a pitch angle (between the centers of thesurface areas of the iron pieces on the permanent magnet 14's side) ofabout 25.7 degrees (about one fourteenth of the circumference whosecenter is the rotation axis 12).

The fourteen first iron pieces 60 are arranged alternately with thefourteen second iron pieces 62. Specifically, the fourteen first ironpieces 60 and the fourteen iron pieces 62 are spaced at a pitch of about12.9 degrees (one twenty-eighth of the circumference). Likewise, thetwenty-eight iron pieces that surround the second coil 58 are spaced ata pitch of about 12.9 degrees.

Next, there will be described a positional relationship between thefirst yoke 66 that surrounds the first coil 60 and the second yoke 68that surrounds the second coil 58. The twenty-eight iron pieces thatsurround the first coil 56 are spaced at a pitch of about 12.9 degreesaround the rotation axis 12. The twenty-eight iron pieces that surroundthe second coil 58 are so arranged that their centers come between theiron pieces that surround the first coil 56.

Specifically, the second yoke 68 is shifted at about 6.4 degrees (onefifty-sixth of the circumference whose center is the rotation axis 12)from the first yoke 66. In other words, the iron pieces that surroundthe first coil 56 and the iron pieces that surround the second coil 58are so arranged around the rotation axis 12 that they are shifted at anangle of about 6.4 degrees from each other.

The first iron pieces 60 and the second iron pieces 62 are providedclosely to the inside perimeter of the ring-shaped permanent magnet 64.This permanent magnet 64 has a total of twenty-eight magnetic poles.Fourteen north poles and fourteen south poles are arranged alternately.The magnetic poles of this permanent magnet 64 are arranged in parallelwith the axial direction of the rotation axis 12.

As shown in FIG. 10, this permanent magnet 64 is composed of fourpermanent magnets shaped like an arc of a quarter circle in combinationand covers the first iron pieces 60 of the first coil and the secondiron pieces 62 of the second coil 58.

The permanent magnet 64 that covers the first coil 56 and the secondcoil 58 applies magnetic fields to the first iron pieces 60 and thesecond iron pieces 62. When the rotation axis 12 is turned, thealternately arranged magnetic poles of the permanent magnet 64 applyalternately different magnetic fields to the first iron pieces 60 andthe second iron pieces 62, and thereby the directions of magnetic fluxesthat cross the first coil 56 and the second coil 58 are alternatelychanged. This causes the first coil 56 and the second coil 58 tosuccessively produce electromotive force. During one turn of therotation axis 12, the directions of the magnetic fluxes crossing thefirst coil 56 and the second coil 58 is changed 28 times.

Further, the permanent magnet 64 is fixed to the rotation axis 12through a case (not shown) that covers the permanent magnet 64 and abearing (not shown). In this case, the permanent magnet serves as astator, and a combination of the first coil 56 and the first yoke 66 anda combination of the second coil 58 and the second yoke 68 are served asa rotator.

A function of the fifth embodiment will be described. In the fifthembodiment, the iron pieces of the respective coils around the rotationaxis 12 do not correspond to each other. Therefore, the maximum coggingtorques, which are generated, when the respective iron pieces aremagnetized by the permanent magnet 64 are generated on differentposition.

Therefore, compared to the case where the positions of the iron piecesof the first yoke 66 that covers the first coil 56 correspond to thoseof the iron pieces of the second yoke 68 that covers the second coil 58,the maximum value of the cogging torque is reduced in the case of theelectric generator 10 according to the fifth embodiment. In addition,since the cycle of the maximum cogging torque is halved, a smoothrotation of the rotation axis 12 can be realized.

In the fifth embodiment, the position where the maximum cogging torqueis generated is changed by arranging the iron pieces that cover thefirst coil 56 and the iron pieces that cover the second coil 58 in astaggered configuration. However, instead of arranging the iron piecesin a staggered configuration, the magnetic poles of the permanent magnet64 that provide magnetic flux to the iron pieces that cover the firstcoil 56 and the second coil 58 may be arranged in a staggeredconfiguration. Further, the number of combinations of the coil and ironpieces that are mounted on the same rotation axis 12 are not limited totwo. The number of combinations of the coil and the iron pieces thatcover the coil can be increased within an acceptable range for design.

While five embodiments of the present invention have thus beendescribed, it should be understood that the present invention be notlimited to these embodiments. Various changes, modifications, andimprovements can be made to the embodiments on the basis of knowledge ofthose skilled in the art without departing from the scope of the presentinvention.

INDUSTRIAL APPLICABILITY

As described above, in the present invention, the attracted pieces areprovided to such positions that correspond to the positions between thefield iron pieces that apply the magnetic field to the coil, so that theattractive force exerted to the attracted pieces by the permanent magnetcan be used to stimulate the rotation of the rotation axis. Therefore,the resistance of the cogging torque to the rotation axis is reduced.Further, since the time that the rotation axis is affected by thecogging torque is shortened, abnormal vibration or noise of the electricgenerator is decreased. For this reason, when the electric generator ofthe present invention is used in the bicycle, wheels can be smoothlyturned.

Further, since the cycle of the maximum cogging torque is shortened byproviding the attracted pieces and variations of the cogging torque arereduced, the rotation axis can be smoothly rotated.

Furthermore, in the present invention, a plurality of wire wound means(a combination of the field iron pieces and the coil) can be provided.In this case, the field iron pieces and the attracted pieces arereplaced with two wire wound means. For example, one permanent magnet isshared between two wire wound means. If the iron pieces of the one wirewound means and the iron pieces of the other wire wound means arestaggered, the maximum vale of the cogging torque is not increased.Therefore, the rotation axis can be smoothly rotated. In this case, whenthe two wire wound means are connected in series, the maximum voltage isthe square root of 2 times the maximum voltage of single wire woundmeans. In other words, although the rotation axis is rotated by the samepower, the maximum voltage can be the square root of 2 times as that ofthe single wire wound means.

Furthermore, in the present invention, a plurality of electricgenerating means (combination of coil, yoke, and permanent magnet) inwhich the positions where the maximum cogging torque is generated aredifferent are mounted on the rotation axis, so that the time that therotation axis is affected by the cogging torque is shortened andtherefore the rotation axis can be smoothly rotated. In addition, sincethe cycle of the maximum cogging torque is shortened, the rotation axiscan be smoothly rotated.

When the electric generator of the present invention is used for a windpower generator, the effect of the cogging torque on the rotation axisis reduced, so that a rotator can be rotated by a slight breeze. Inaddition, since a rotator can be rotated by light wind, the electricgenerator of the present invention can be used effectively in a lightwind area as a wind power generator.

1. An electric generator comprising: a permanent magnet composed ofmagnetic poles arranged radially and alternately around a rotation axis;a coil wound around an electrically insulated bobbin; a plurality ofmetal pieces, rotating relatively to the permanent magnet and applyingmagnetic flux generated by the permanent magnet to the coil; andattracted means having a plurality of attracted pieces, said attractedpieces arranged radially around the rotation axis and magnetized by thepermanent magnet, wherein said attracted pieces of the attracted meansare placed in such positions that they do not correspond to the metalpieces.
 2. An electric generator comprising: a permanent magnet composedof magnetic poles arranged radially and alternately around a rotationaxis; a coil wound around an electrically insulated bobbin; a pluralityof metal pieces, rotating relatively to the permanent magnet andapplying magnetic flux generated by the permanent magnet to the coil;and attracted means having a plurality of attracted pieces, saidattracted pieces arranged radially around the rotation axis andmagnetized by the permanent magnet, wherein said attracted pieces of theattracted means are placed in positions that correspond to positionsthat bisect spaces between the metal pieces.
 3. An electric generatorcomprising: a permanent magnet composed of magnetic poles arrangedradially and alternately around a rotation axis; and two wire woundmeans composed of a coil wound around an electrically insulated bobbinand a plurality of metal pieces, said metal pieces rotating relativelyto the permanent magnet and applying magnetic flux generated by thepermanent magnet to the coil, wherein the metal pieces of one of saidwire wound means are placed in such positions that they do notcorrespond to the metal pieces of the other wire wound means.
 4. Anelectric generator comprising: a permanent magnet composed of magneticpoles arranged radially and alternately around a rotation axis; and twowire wound means composed of a coil wound around an electricallyinsulated bobbin and a plurality of metal pieces, said metal piecesrotating relatively to the permanent magnet and applying magnetic fluxgenerated by the permanent magnet to the coil, wherein the metal piecesof one of said wire wound means are placed in positions that correspondto positions that bisect spaces between the metal pieces of the otherwire wound means.
 5. An electric generator comprising: a plurality ofelectric generating means having a permanent magnet composed of magneticpoles arranged radially and alternately around a rotation axis, a coilwound around an electrically insulated bobbin, and a plurality of metalpieces rotating relatively to the permanent magnet and applying magneticflux generated by the permanent magnet to the coil, wherein the metalpieces of any one of said electric generating means are placed in suchpositions that they do not correspond to the metal pieces of the rest ofthe electric generating means.
 6. An electric generator comprising: aplurality of electric generating means having a permanent magnetcomposed of magnetic poles arranged radially and alternately around arotation axis, a coil wound around an electrically insulated bobbin, anda plurality of metal pieces rotating relatively to the permanent magnetand applying magnetic flux generated by the permanent magnet to thecoil, wherein the metal pieces of any one of said electric generatingmeans are placed in positions that correspond to positions that bisectspaces between the respective metal pieces of the rest of the electricgenerating means.
 7. An electric generator comprising: a plurality ofelectric generating means having a permanent magnet composed of magneticpoles arranged radially and alternately around a rotation axis, a coilwound around an electrically insulated bobbin, and a plurality of metalpieces rotating relatively to the permanent magnet and applying magneticflux generated by the permanent magnet to the coil, wherein the magneticpoles of any one of said electric generating means are placed in suchpositions that they do not correspond to the magnetic poles of the restof the electric generating means.
 8. An electric generator comprising: aplurality of electric generating means having a permanent magnetcomposed of magnetic poles arranged radially and alternately around arotation axis, a coil wound around an electrically insulated bobbin, anda plurality of metal pieces rotating relatively to the permanent magnetand applying magnetic flux generated by the permanent magnet to thecoil, wherein the magnetic poles of any one of said electric generatingmeans are placed in positions that correspond to positions that bisectspaces between the respective magnetic poles of the rest of the electricgenerating means.
 9. The electric generator according to claim 1,wherein said permanent magnet is a cylindrical-shaped permanent magnetcomposed of magnetic poles arranged radially and alternately around therotation axis, and said plurality of metal pieces and said attractedpieces of the attracted means are close to the outer perimeter of thepermanent magnet.
 10. The electric generator according to claim 3,wherein said permanent magnet is a cylindrical-shaped permanent magnetcomposed of magnetic poles arranged radially and alternately around therotation axis, and said plurality of metal pieces are close to the outerperimeter of the permanent magnet.
 11. The electric generator accordingto claim 1, wherein said permanent magnet is a ring-shaped permanentmagnet composed of magnetic poles arranged radially and alternatelyaround the rotation axis, and said plurality of metal pieces and saidattracted pieces of the attracted means are close to the insideperimeter of the permanent magnet.
 12. The electric generator accordingto claim 3, wherein said permanent magnet is a ring-shaped permanentmagnet composed of magnetic poles arranged radially and alternatelyaround the rotation axis, and said plurality of metal pieces are closeto the inside perimeter of the permanent magnet.